1. Field of the Invention
This invention relates to carburetors for internal combustion engines and more particularly to improved starting means of a carburetor of the type which includes a starting suction conduit for supplying a fuel-air mixture to the internal combustion engine when the engine is started and warmed up, in addition to a main suction conduit for supplying a fuel-air mixture to the engine after completion of warm-up.
2. Description of the Prior Art
A carburetor having a main suction conduit and a starting suction conduit is known as from Japanese Utility Model Publication No. 12822/77. This type of carburetor generally comprises a main suction conduit, a control throttle mounted in the main suction conduit, a main fuel passage for the main suction conduit, a main air bleed passage for the main fuel passage, a starting suction conduit, a starting fuel passage for feeding a fuel to the starting suction conduit, and a valve mounted in the starting suction conduit. In this type of carburetor, if the degree of opening of the control throttle is increased when the warm-up of the engine is not completed yet after the engine is started, then the suction pressure increases in a portion of the main suction conduit which is disposed downstream of the control throttle where the starting suction conduit opens in the main suction conduit. This causes a reduction in the quantity of a fuel-air mixture supplied through the starting suction conduit, with the result that the fuel-air mixture supplied to the engine becomes lean even if the control throttle is opened to permit the fuel to be supplied through the main fuel passage. Thus the mixture supplied to the engine becomes too lean to operate the engine which is not fully warmed up yet. As a result the problem of cessation of fuel combustion or deterioration of the acceleration ability during operation of the engine is raised.
To cope with this situation, it has hitherto been common practice to use a method wherein the fuel-air ratio is compensated more than is necessary to enrich the fuel-air mixture, so as to thereby increase the range in which the fuel-air mixture can have its proportions of fuel and air compensated in accordance with an increase in the volume of air intake. However, this method has the disadvantages that it is not economical to use this method because fuel consumption increases in the vicinity of the minimum air volume, and that the correction of the fuel-air ratio is not carried out satisfactorily except in the vicinity of the minimum air volume.